Prelati's Spellbook: Textbook of the Sunken Spiral Castle (螺湮城教本プレラーティーズ・スペルブック, Rain-jō KyōhonPurerātīzu Superubukku?) is a demonic guidebook and summoning grimoire with a cover made of glistening and wet human skin. It is also known as the R'lyeh Text in reference to H. P. Lovecraft's Cthulhu Mythos. It was probably copied from the original book in the sunken spiraled castle, translated from the R'lyeh language into Chinese during the Xia Dynasty, and later translated into Italian by François Prelati. Furthermore, the previous original text was described in a language other than that of humanity's languages. The book contains records of a forbidden knowledge relating to an evil god of an ancient time sometime before humanity's origin.